Logical node identification in an information transmission network

ABSTRACT

A system for generating and sending a Logical Node identification signal as part of a data stream is disclosed. The system also includes subscriber stations capable of receiving and extracting Logical Node identification information from a data stream. The subscriber stations create new messages including the Logical Node identification signal and send the message to the transmission network system control, such that switching of data streams to an appropriate channel over the information transmission network is done consistent with the network topology.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/436,934, filed on Nov. 8, 1999.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to the field of informationtransmission networks and more specifically to Logical Nodeidentification of such networks. More particularly, the presentinvention relates to Logical Node identification of such networkssupporting session based routing/switching of information flow inheterogeneous networks.

[0004] 2. Description of the Background Art

[0005] In the field of information transmission, routing and switchingof information to the destination node is most commonly accomplished inone of two approaches: (1) symmetric switched virtual paths/circuits(i.e., ATM) or (2) packet-based routed networks (i.e. Internet). A thirdtype of information routing/switching network exists in many forms thatcan be better supported through a variant of the two approaches withasymmetric switched virtual paths/circuits or asymmetric packet basedrouting.

[0006] This third area can be classified into two categories: first, theset of information transmission networks that require a combination ofthe packet routed networks tightly coupled with asymmetric switchednetworks (i.e. interactive multimedia content delivery such as invideo-on-demand that requires a streaming network flow for video andaudio and usually an Out Of Band IP network to handle the interactivitybetween the source and destination); second, the set of informationtransmission networks that can improve network latency by takingadvantage of the knowledge of the point of access in packet basednetworks (i.e., dynamic routing changes necessary to support uniqueroving lap top computers). The present application will address thisfirst case.

[0007] The former category of information transmission networks is whatthe present invention will address in detail. In particular, theinteractive multimedia service of video-on-demand over Hybrid Fiber Coax(HFC) networks is currently in existence for cable services. In thiscase, there exists unidirectional content streaming (QAM modulated videoand audio streaming of content to the digital set top box in the home)and IP based interactivity (via Out Of Band downstream to the home and avaried Return Path packet forwarding connectivity from the subscriber'sset top box to the cable headend equipment). This same solution can beused for satellite broadcast (content delivery) with wireless (cellphone) or telephone modem for interactivity; as well as for terrestrialbroadcast systems (e.g. MMDS, LMDS). It is also noted that the controlsession via the Out Of Band could also be multiplexed into the streaminglink in the In Band.

[0008] A technique to increase the number of video-on-demand programsthat can be concurrently transmitted is by channel reuse, where programsare assigned to channels at an intermediate node (typically referred toas a “remote headend” or “hub”) where lines from individual subscriberstations are coupled to the main CATV network. For the purposes of thepresent invention, the term “headend” is defined as any physical sitewhere modulation, demodualtion, and processing (controlling, monitoring,etc.) equipment are kept and operated whether they be staffed with humanoperators or unstaffed sites that are remotely monitored whether theyrelate specifically to Cable or other transmission means such as MMDS.This technique allows the same channels to be assigned to differentprograms at different nodes (known as spectrum reuse through physicalmedia partitioning). Thus, dedicated video-on-demand channels cantransmit programs to one set of subscriber stations coupled to a firsthub, while the same channels can be used to transmit a different set ofprograms to another set of subscriber stations coupled to a second hub.

[0009] Typically, provision of video-on-demand services is implementedby assigning a session control manager (SCM) to one or more hubs. TheSCM is responsible for receiving requests from set-top boxes atassociated hubs and providing the requested services. Each SCM must thenbe informed of the subscriber stations corresponding to the assignedhub. Based on this topological information, the SCM provides theinformation for the creation of a virtual circuit from the video serverto the QAM modulator, and thus an access mechanism to the video andaudio stream from the set top box. The SCM also tells the set top boxwhich frequency to tune the demodulator and which packet identificationnumbers (PIDs) to filter for the video and audio streams.

[0010] If subscriber stations are added or deleted, such as by new orcanceled subscriptions, then the mapping between SCMs, hubs, and set topboxes may need to change. For example, a set of QAM channels can onlyaccommodate a certain number of subscriber stations. If the number ofsubscriber stations on a hub exceeds the capacity of the allocatedstream, then further Logical Node partitioning may occur on the hub.While such changes can be made to the mapping information in the headendmanually, it is desirable to have a more efficient and automated methodfor re-assigning channels for node usage.

SUMMARY OF THE INVENTION

[0011] In a principal aspect, the present invention provides automatictransmission to subscriber stations of information about correspondingsession control managers and coupling of channel groups defined asnodes.

[0012] In accordance with the principles of the present invention, avideo-on-demand (VOD) system includes a plurality of session controlmanagers to cause transmission of a requested program to a requestingsubscriber station. The video-on-demand system is coupled to a pluralityof subscriber stations by a network capable of spectrum reuse betweenthe subscriber station and a corresponding one of a plurality of nodesdisposed between the video-on-demand system and the subscriber station.The video-on-demand system comprises a Logical Node assignor whichassigns a logical identification to each of the nodes to identify acorrespondence between each of the nodes and a corresponding one of thesession control managers. For example, a Logical Node for HFC is definedas the group of Fiber Nodes that share the same QAM modulation spectrum.I.e. same streams in VOD channels.

[0013] In accordance with further aspects of the invention, the LogicalNode assignor periodically transmits node assignment information to eachof the nodes in the network to uniquely identify the Logical Node andalso identify a corresponding session control manager for each of thenodes. This allows for the subscriber stations tune to this digitalchannel at any time and get these information on a timely basis.Advantageously, such techniques allows automatic dissemination ofinformation regarding mapping between session control managers, LogicalNodes, and subscriber stations. The result is reduced complexity andoverhead in managing a video-on-demand system, thereby reducing overallcosts.

[0014] The principles of the present invention are particularlyadvantageous in Hybrid Fiber Coaxial (HFC) systems used for transmissionof video programming. However, the principles described herein may alsobe used in direct broadcast satellite (DBS) systems, Local Multi-PointDistribution Services (LMDS), and Multi-channel Multiunit DistributionSystems (MMDS).

[0015] One particular advantage of the present invention, is thatbecause of the automatic identification of the Logical Node to whicheach subscriber station is associated, the present invention allows forswitching the unicast VOD stream to the correct QAM modulator thatmodulates to the Logical Node for receipt by the subscriber station.This is particularly advantageous as new Logical Nodes can be created orexisting nodes are divided because of increasing demand for subscriptionand service.

[0016] These and other features and advantages of the present inventionmay be better understood by considering the following detaileddescription of a preferred embodiment of the invention. In the course ofthis description, reference will frequently be made to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a block diagram of a general embodiment of a systememploying the principles of the present invention.

[0018]FIG. 2A is a block diagram of a first embodiment of the systememploying the principles of the present invention where a broadcastsatellite is used as a portion of the transmission network.

[0019]FIG. 2B is a block diagram of a second and preferred embodiment ofthe system employing the principles of the present invention where anvideo-on-demand network is used as the transmission network.

[0020]FIG. 3 is a high-level block diagram showing a headend includingsession control mangers, the hubs and the subscriber stations of thesecond embodiment in more detail.

[0021]FIG. 4 is a high-level block diagram showing the session controlmangers, the hubs and the subscriber stations of FIG. 3 and the LogicalNodes into which they are divided in more detail.

[0022]FIG. 5 is a flowchart of a general method for transmitting LogicalNode identification signals and using them to configure the system andtransmit data signals.

[0023]FIGS. 6 and 7 are flowcharts showing operation of the system inaccordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Referring now to FIG. 1, a preferred embodiment of a system 100 aconstructed in accordance with the present invention is shown. Thesystem 100 a preferably comprises: a Logical Node Identification (ID)generator 102, a signal source 104, a combiner 106, an informationtransmission network 108, and an information distributor 110. Thepresent invention is particularly advantageous because it inserts aLogical Node identification signal into the data stream. This LogicalNode identification signal is transmitted through the network 108, andthen retransmitted back to the SCM 224 (See FIG. 2B) for determining theprecise configuration of the system 100 a.

[0025] This first embodiment illustrates the most general implementationof the present invention, and therefore, will be described here in onlygeneral terms. FIGS. 2A and 2B illustrate more particular embodiments ofthe present invention for specific transmission networks and will bedescribed with more particularity.

[0026] The Logical Node ID generator 102 produces at least one uniqueLogical Node identification number and transmits the uniqueidentification number as a signal at the output of the Logical Node IDgenerator 102. Preferably, the Logical Node ID generator 102 producesplurality of unique identifiers which are sent to the combiner 106 andcombined with other information according to which node or location towhich the information is being transmitted. The output of the LogicalNode generator 102 is coupled to an input of the combiner 106. A signalsource 104 providing video, sound or data signals such as in a digitalvideo signal is provided at the output of the signal source 104, andalso provided to the combiner 106. The output of the signal source 104is coupled to the second input of the combiner 106.

[0027] The combiner 106 has one more outputs coupled to an informationtransmission network 108 for transmitting a combined signal thatincludes an address for the information, content from the signal source104, and the Logical Node ID signal from the Logical Node ID generator102 to the information distributor 110 coupled at the remote end of thetransmission network 108. In the preferred embodiment, the transmissionnetwork 108 includes one or more stream channels 202 for transmittinginformation from the combiner 106 to the devices downstream on theremote end of the information transmission network 108. The informationtransmission network 108 also includes configuration control channels204 for sending signals along a reverse path between the informationdistributor 110 and combiner 106.

[0028] The information distributor 110 is coupled to send and receivesignals over the information transmission network 108. The informationdistributor 110 is also coupled to a plurality of devices (not shown)such as set top boxes by a plurality of signal lines 120-132. Theinformation distributor 110 receives the streaming channels and sendsthe source signal and the Logical Node ID down a corresponding one ormore signal lines 120-132 according to the node ID number. For example,a group of signals sent over the information transmission network 108and received by the information distributor 110 having video content anda Logical Node ID number of 1 would be transmitted only over signal line120. Such video content and a Logical Node ID are not transmitted overother signal lines 122-132 for nodes 2-n. Other combined signals wouldbe similarly sent over the respective signal lines 122-132 correspondingto their Logical Node identification number. As shown, an individualLogical Node identification number such as Logical Node 4, maycorrespond to a plurality of signal lines such as signal lines 126, 128,130. In one embodiment, the signal lines 120-132 may be constructed ofhybrid/fiber coax. Thus, the information distributor 110 effectivelyseparates the data streamed over the streaming channels 202 fordistribution over individual signal lines or groups of signal linesconsistent with channel reuse.

[0029] The information distributor 110 also receives a plurality ofsignals sent upstream by devices (not shown) to the informationdistributor 110. The information distributor 110 in turn sends thesignals over the configuration and control channels 204 to the combiner106. In this manner, a particular set top box (STB 220 see FIG. 2B) orsubscriber station can receive a signal including the Logical Node ID,incorporate the Logical Node ID along with a signal identifying thesubscriber station, and send the incorporated signal upstream throughthe information distributor 110 and configuration and control channels204 to the combiner 106. Using this information, the SCM 224 determinethe exact configuration of the network and nodes, make necessary changes(e.g. create new nodes, eliminate node or combine nodes) to maximize theusage of the network bandwidth.

[0030] Referring now to FIG. 2A, a second embodiment 100 b of the systemconstructed in accordance with the present invention is shown. In thesecond embodiment 100 b, like components having the same functionalityhave been labeled with like reference numeral for ease of understandingand convenience. The second embodiment 100 b includes the Logical NodeIdentification (ID) generator 102, the signal source 104, the combiner106, and a transmission network in the form of a streaming channel 202 aand a return channel 204 a. The information distributor takes the formof a receiver and descrambler 210 a, and a telephone 214 a.

[0031] The Logical Node Identification (ID) generator 102, the signalsource 104, the combiner 106 are the same as has been described abovewith reference to FIG. 1. However, in this embodiment, the combiner 106transmits the combined signal to a one or more base satellite stationsfor uploading to a satellite. The satellite in turn receives andtransmits the combined signal including the Logical Node ID to thereceiver and descrambler 210 a. While only one receiver and descrambler210 a is shown per satellite, those skilled in the area will realizethat there are preferably many receivers and descramblers 210 a for eachsatellite.

[0032] The receiver and descrambler 210 a receives the combined signalfrom the satellite, descrambles the signal and sends the combined signalto one or more devices 212 a coupled to the receiver and descrambler 210a. The receiver and descrambler 210 a is also coupled by a telephone 214a-214 n and a phone line 204 a-204 n to the combiner 106. The paththrough the telephone and a public switched network provides the returnpath. Those familiar in the art will recognize that the telephone 214a-214 n and phone line 204 a-204 n could be a cell or wirelesstelephone. Thus, the receiver and descrambler 210 a is able tocommunicate with the devices 212 a to determine channel selection andnode ID and send that information back to the combiner 106 via thetelephone line 204 a-204 n. In this manner, the system 100 b may definea plurality of Logical Nodes, change or modify the nodes as desired andconfirm the network configuration through use of the Logical Node IDsignal inserted by the combiner 106 and returned by the device 212 a-212n and the receiver and descrambler 210 a-210 n.

[0033] Referring now to FIG. 2B, a third and preferred embodiment of asystem 100 c constructed in accordance with the present invention isshown. The third embodiment 100 c uses the capabilities of a traditionalcable system to provide the streaming channel 202 b and the returnchannel provided with video-on-demand systems as the return path. Thethird embodiment 100 c preferably comprises a Logical NodeIdentification (ID) generator 102 b, a video server 104 b as the signalsource, a combiner in the form of a digital video modulator (DVM) module106 b, the optical fiber 202 b as the transmission network, a controlchannel modem (CCM) 222 and a session control manager (SCM) 224providing the return path 204 b, and an information distributor 110 b.The system 100 c advantageously uses a plurality of DVMs 106 b and eachhas a plurality of channels. Each DVM 106 b preferably provides thevideo streams to different Logical Nodes. Thus, the automaticidentification of the Logical Node in the return channel, allows the SCM224 to determine which video stream and channel provided by which DVMcorresponds to a particular set top box 220. This is particularlyadvantageous because there is routinely a need to re allocated the settop box 220 among Logical Nodes and DVM channels.

[0034] The DVM module 106 b receives video signal from the video server104 b and node ID signals from the Logical Node Identification (ID)generator 102 b. The DVM module 106 b combines these signals andtransmits them over the transmission channel 202 b to the informationdistributor 110 b. The SCM 224 controls the mixing of content providedby the video server 104 b and receives communication over the back orreturn path 204 b via CCM 222. For example, some of these components maybe found at a headend in a typical on-demand cable system. Theinformation distributor 110 b divides the signals received from the DVMmodule 106 b and outputs them over respective signal lines 120-132according to the Logical Node ID assigned to each signal. For example, aplurality of set top boxes 220 a-220 n are coupled to line 120 and formLogical Node 1. Each of the other signal lines 122-132 or groups of thesignal lines are coupled in similar fashion to form Logical Nodes of thenetwork. Such any exemplary system is described in more detail in U.S.Pat. No. 6,253,375, issued Jun. 26, 2001, entitled “System ForInteractively Distributing Information Services,” filed Dec. 4, 1997,which is incorporated herein by reference.

[0035] In this third embodiment 100 c, the Logical Node generator ispreferably part of a transport processing module 102 b. The transportprocessing module (TPM) 102 b adds control signals and data to thestreams generated by the DVMs 106 b. The TPM 102 b is preferably coupledto the session control manager 224 and to the CCMs 222 through the VMEbus architecture. The TPM 102 b is also coupled to the DVM module 106 bto provide for in-band communication. More specifically, the TPM 102 balso adds identification information to the video and audio contentprovided by the server 104 b such as program specific information (PSI)and packet identification numbers (PIDs).

[0036] In FIG. 3, a plurality of subscriber stations 305-308 are coupledby an information transmission network 302 to a cable headend 304 forreceiving video programming services. The subscriber stations 305-308preferably take the form of a digital set-top box capable of requestingvideo programming from the headend 304. However, the subscriber stations305-308 can take other forms to provide information from network 302 todifferent types of output devices, e.g. cable modems with personalcomputers and ADSL modems with set top boxes. The subscriber stations305-308 are shown generally and each shown subscriber station 305-308represents a plurality of subscriber stations.

[0037] The headend 304, which is shown only in very general form,includes the necessary equipment and capability to provide subscriberstations 305-308 with on demand services such as, for example,video-on-demand services where a user requests a particular moviethrough a subscriber station and the headend 304 responds bytransmitting data representing the movie to the requesting subscriberstation for viewing by the user. Included within the headend 304 are aplurality of session control managers (SCMs) 314, 315, 316 and 317. TheSCMs perform various system command and control functions as well ascommunicating the requested programming in the form of a data stream tothe transmission network 302. The SCMs 314, 315, 316 and 317 havecapability to address the streams to be propagated to the subscribers inbroadcast, multicast or unicast modes. As used herein, the term“broadcast” means transmission of data for receipt by all subscriberstations on the network. “Unicast” means transmission of data forreceipt by only a single subscriber station on the network, and“multicast” means transmission of information for receipt by more thanone but less than all subscriber stations on the network.

[0038] Specifically, each SCM 314-317 transmits video signals to thesubscriber stations over an information channel in network 302 bymodulating a base band data stream onto a carrier signal and upconverting the signal to a transmission frequency that complies with aconventional CATV frequency spectrum. By way of example, a downstreamdata modulation performed by a SCM can be a 64-ary Quadrature AmplitudeModulation (QAM) and the transmission frequency can be in the range of54-860 MHz. These techniques are merely exemplary of a typicaltransmission mechanism and other modulation types and frequency bandsmay be used.

[0039] The SCMs 314-317 transmit control information to the subscriberstations 305-308 via a downstream command channel in transmissionnetwork 302. By way of example, such control information can befrequency multiplexed with the information channel to effecttransmission on a carrier in the range of 54-860 MHz using a 1 MHzbandwidth. The subscriber stations 305-308 communicate with acorresponding SCM 314-317 via a reverse (back or upstream) channel. Inan exemplary embodiment, each SCM 314-317 supports 16 such reversechannels. Each reverse channel carries, for example, a BPSK modulatedsignal on a carrier in the range of 5-42 MHz, where the channel capacityis approximately 64 Kbps. The exact frequency ranges, modulation typesor channel capacities are not critical and can be varied. Furtherdetails of the operation of the SCMs 314-317 and other components of theheadend 304 to provide VOD services are described in U.S. Pat. No.6,253,375, issued Jun. 26, 2001, and entitled “System for InteractivelyDistributing Information Services”, and assigned to the assignee of thepresent application, which is hereby incorporated by reference in itsentirety.

[0040] The transmission network 302 preferably takes the form of aHybrid Fiber Coaxial (HFC) network in which the headend 304 is coupledto the hubs 309-312 by fiber optic cabling. The hubs 309-312 are coupledto corresponding subscriber stations by coaxial cabling. Each hub309-312 typically has capability to support hundreds to thousands ofsubscriber stations. The hubs 309-312 are preferably of conventionaltype.

[0041] The VOD service employs a number of predetermined channels in theinformation channel to transmit the requested video programs. By way ofexample, the number of channels available for use by the VOD service canbe 2, 4, or 8 analog channels. The network 302 and headend 304 implementspectrum reuse at the hubs 309-312 to increase the number of channelsavailable for the VOD service.

[0042] Each of the Logical Nodes (VOD channels per hubs 309-312) have acapability to service a limited number of subscriber stations. Thenumber of Logical Nodes required is therefore roughly proportional tothe number of subscribers being serviced by the system 100 c. By way ofexample, each 64-QAM channel typically can service up to 80 subscribers.Depending upon the number of subscriber stations coupled to a particularhub 309-312, a particular Logical Node may service only a portion of thesubscriber stations on a hub, may service all of the subscriber stationson a hub but no more, or may service subscriber stations on more thanone hub. Each of these scenarios is shown in FIG. 3. For example, SCM314 services subscriber stations on hubs 309 and 310. This wouldtypically occur in a situation where the hubs 309 and 310 are not fullypopulated with subscriber stations 305, 306 or where initial servicepenetration is low. SCM 315 services only subscriber stations 308 on hub312. Hub 311 has associated therewith SCMs 316 and 317 for servicingsubscriber stations 307. This situation arises where a hub has coupledthereto, a number of subscriber stations that exceed the capacity of aparticular SCM and requires many Logical Nodes. As the number ofsubscriber stations increases or decreases for a particular hub, themapping between SCMs Logical Nodes, and subscriber stations may need tochange. For example, this may happen if new homes are built or ifexisting subscribers cancel subscriptions to services offered by headend304 or if new subscribers are added.

[0043] In accordance with the principles of the present invention, SCMs314-317 can be automatically allocated to subscriber stations 305-308based on the changing topology of the network 302 and its associatedsubscriber stations. Advantageously, this is performed by determiningthe number of subscriber stations coupled to each hub, and transmittinga Logical Node identifier (ID) to each subscriber station. The LogicalNode ID provides a correspondence between an SCM and correspondingsubscriber stations. For example, in FIG. 4, subscriber stations 305 and306 correspond to a first Logical Node from nodes 1-4, subscriberstations 307 correspond at least two (third and fourth) Logical Nodesand from nodes 11-20 and the other from nodes 21-n, and subscriberstations 312 correspond to a second Logical Node from nodes 5-10.

[0044] The Logical Node IDs for the subscriber stations on the network302 are preferably determined periodically and periodically transmittedto the subscriber stations. Preferably the Logical Node ID istransmitted as a MPEG-II (Motion Pictures Expert Group, Type II) packetwhich contains appropriate header information together with the LogicalNode ID. MPEG type encoding is a common protocol for encoding video dataand is therefore a convenient protocol for encoding of the Logical NodeID. However, the exact manner in which the Logical Node ID is encodedfor transmission is not critical and other encoding techniques can beused within the principles of the present invention.

[0045]FIG. 4 of the drawings illustrates, by way of the example shown inFIG. 3, the manner in which the Logical Node IDs are transmitted. InFIG. 4, subscriber stations 305 and 306 are part of a first LogicalNode. This information is provided to subscriber stations 305-306 bytransmitting Logical Node ID 1 from headend 304 to subscriber stations305-306. Subscriber stations 308 are part of second Logical Node. Thisinformation is provided to subscriber stations 308 by transmittingLogical Node ID for this second Logical Node from headend 304 tosubscriber stations 308. Subscriber stations 307 are either part of athird Logical Node or fourth Logical Node. The corresponding nodeinformation (third Logical Node ID or fourth Logical Node ID) istransmitted to the appropriate subscriber stations 307.

[0046] The introduction of the Logical Node ID into the video stream andits use to identify the channels servicing a particular subscriberstation are particularly advantageous. The provision of Logical Node IDsignals in the video stream allow the subscriber stations to be movedanywhere in the network and get the video streams switched to thesubscriber station based on a new Logical Node ID. For example, aparticular subscriber station may be initially connected to the networkand assigned to Logical Node ID 1. All the information for thesubscriber including information particular to the subscriber station isprovided. However, the user may move geographically, take the subscriberstation and attempt to gain access from a new location being service bya different Logical Node. Since the ID of the different Logical Node ispart of the stream, once it is provided to the relocated subscriberstation, the headend 304 will know which channels to provide signalsintended for the user. This eliminates any manual reconfiguration of thenetwork that is required in the prior art. Rather with the presentinvention, the service can be updated by simply updating channel and DVMinformation in the SCM. Other examples where the provision of theLogical Node ID is particularly advantageous is where new nodes arecreated or eliminated by changes in the number of subscribers usingparticular channels. The use of Logical Node ID eliminates the need forany changes in manual configurations.

[0047] Referring now to FIGS. 5-7, the methods of the present inventionfor sending and using a Logical Node ID signal as part of streaming datawill be described in more detail. The general method will first bediscussed with reference to FIG. 5. Then a method for using the LogicalNode ID to determine the appropriate channel on which to transmit arequested program is described in two embodiment with reference to FIGS.6 and 7.

[0048] As shown in FIG. 5, the method for inserting, transmitting andusing the Logical Node ID in accordance with the present invention isshown. The process begins in step 502 by generating a unique LogicalNode ID for each node and inserting such Logical Node ID into the datastream. Then in step 504, the Logical Node ID signal is transmitted aspart of the data stream over the information network 108. Next, in step506, the data stream including the Logical Node ID is received at asubscriber station. Then in step 508, the subscriber station uses theLogical Node ID received to create a new message which includes theLogical Node ID. The message created in step 508 is then sent in step510 to the headend. The combiner or headend sets the Logical Nodemembership using this message in step 512, and thus, the topology of thenetwork is known by the system 100 c. The system 100 c can then use theinformation stored at the headend to switch data streams using the TPM102 b and DVM module 106 b such that programs will be correctly routedeven though changes may have been made to the network manually orautomatically. In other words, using the Logical Node ID the TPM 102 band DVM module 106 b can be assured to send data to the appropriatesubscriber stations.

[0049]FIG. 6 is a flowchart showing an embodiment where the role of themaster SCM in identifying the corresponding SCM and the role of the hubin providing the channel allocation information to the subscriberstation are eliminated. Advantageously, elimination of such actionsreduces the amount of time (and accompanying bandwidth) required toinitiate VOD service. These steps are eliminated by storing the addressof the corresponding SCM together with the channel allocationinformation in the subscriber station. This information can be stored inthe subscriber station in a nonvolatile memory such as a flash memory astypically found on subscriber stations such as digital set-top boxes.

[0050] Turning to FIG. 6, at step 602, the user requests VOD by way ofthe corresponding subscriber station. At step 604, the subscriberstation reads the Program Map Table (PMT) and at step 604 receives theperiodic transmission of the Logical Node ID. At step 608, the IPaddress of the SCM, which is stored in the subscriber station and itslistener port number are used to make a User Datagram Protocol (UDP orTCP—Transmission Control Protocol) connection between the SCM and thesubscriber station. At step 610, the program transmission occurs untiltermination at step 612.

[0051]FIG. 7 is a flowchart showing communication between a set-top box(portion of a subscriber station) and the headend 304 to request and toreceive video-on-demand (VOD) services, such as transmission of moviesor other video programs. At step 702, the user requests VOD services, byentering appropriate inputs into the set-top box. At step 704, thecorresponding hub responds to the request for VOD service byidentifying, from information stored in the hub, an SCM that isfunctioning as a master SCM. At step 708, the subscriber stationinitiates communication with the master SCM to establish a connectionbetween the master SCM and the subscriber station. This connection ispreferably established in accordance with the User Datagram Protocol(UDP) of the TCP/IP suite of protocols. At step 710, the hub allocates achannel for transmission of the requested video program from thecorresponding hub to the subscriber station. Also at step 710, themaster SCM allocates a program identifier (PID) to uniquely identify therequested program. Transmission of the Logical Node ID at step 712 isperformed periodically, such as for example, every one-tenth of asecond, and the Logical Node ID can therefore be expected to be receivedby the subscriber station. In an alternate embodiment shown in FIG. 7 bydashed lines, the channel for transmission of the requested videoprogram from the corresponding hub to the subscriber station, and theprogram identifier (PID) may be predefined (step 730). For example, acopy of a distributed packet having the predefined channel and PID maybe stored at the subscriber station using local storage to reduce thelatency in starting interactive sessions where the contents providetemporary copies of the information contained in the distributed packet.In such a case, steps 700-710 may be replaced with the single step 730of identifying the predefined channel and PID after which the methodcontinues with that information in step 714.

[0052] Once the subscriber station receives the Logical Node ID, it hasthe necessary information to communicate with the corresponding SCM, andat step 714 the UDP connection between the master SCM and the subscriberstation is terminated. At step 716, a UDP connection is establishedbetween the identified SCM and the subscriber station. Once establishedat 716, transmission of the requested program by the SCM to therequesting subscriber station occurs 718 until the transmission isterminated at step 720.

[0053] It is to be understood that the specific mechanisms andtechniques which have been described are merely illustrative of oneapplication of the principles of the invention. Numerous additionalmodifications may be made to the methods and apparatus described withoutdeparting from the true spirit of the invention.

What is claimed is:
 1. In a hybrid fiber coaxial network forbroadcasting video programs from a headend to a plurality of subscriberstations, the network characterized by hubs for coupling coaxialportions to fiber portions of the network, and further characterized byat least a first and a second channel allocated between each of saidhubs and corresponding subscriber stations, apparatus for responding toa program request from said subscriber stations by causing transmissionof a requested program, comprising: first means for periodicallyproviding a Logical Node identifier, for identifying a correspondencebetween a hub corresponding to said requesting subscriber station and acontrol station; second means, responsive to said program request from arequesting one of said subscriber stations, for providing frequency andPIDs, indicative of said requested program, to said requestingsubscriber station; third means, responsive to said second means, forcausing transmission of said requested program for receipt by saidrequesting subscriber station; and fourth means, for receiving saidlogical node identification from said requesting subscriber station. 2.An apparatus for causing transmission, over a network, of programmingrequested by a subscriber station coupled to the network by way of anetwork controller that assigns a channel for transmission of requestedprogramming from said network controller to said requesting subscriberstation, said network characterized by a first bandwidth between saidapparatus and said network controller, and characterized by a secondbandwidth between said network controller and said subscriber station,said second bandwidth being lower than said first bandwidth, saidapparatus responding to a request by said requesting subscriber stationfor a requested program by causing transmission, for receipt by saidrequesting subscriber station, of a program identifier, which uniquelyidentifies said requested program, and causing transmission, for receiptby said network controller of a logical identifier, which uniquelyidentifies said network controller as a corresponding network controllerand which is independent of physical organization of said subscriberstations on said network, said apparatus further causing transmission,for receipt by said requesting subscriber station, of said requestedprogram, in response to receiving said logical identificationtransmitted by said requesting subscriber station.
 3. The apparatus asset forth in claim 2 further comprising a master control module,responsive to said request by said requesting subscriber station forsaid requested program, for assigning one of a plurality of othercontrol modules to cause transmission of said program identifier, saidlogical identifier and said requested program.
 4. In a video-on-demandsystem having a headend which may be put in communication with asubscriber device via an intermediate node, a method for communicationbetween the headend and the subscriber device, comprising: providingfirst identification information from the headend into a firstdatastream, the first identification information for routingcommunication to the headend; providing the first datastream to theintermediate node; providing the first datastream from the intermediatenode to the subscriber device; in response to receiving the firstdatastream at the subscriber device, using the first identificationinformation in the first datastream to provide a second datastream forthe headend having second identification information, the secondidentification information for routing communication to the subscriberdevice; providing the second datastream to the intermediate node;providing the second datastream from the intermediate node to theheadend; and establishing a session between the headend and thesubscriber device in response to the headend receiving the secondidentification information in the second datastream.
 5. The method ofclaim 4 wherein the headend comprises a session manager.
 6. The methodof claim 5 wherein the intermediate node is associated with a logicalnode.
 7. The method of claim 5 wherein the first identificationinformation comprises an address of the session manager and anidentifier of the logical node.
 8. The method of claim 5 wherein thesecond identification information comprises an identifier of thesubscriber device.
 9. The method of claim 4 wherein the session isselected from a User Datagram Protocol-based session and a TransmissionControl Protocol-bases session.